1. Field of the Invention
The present invention generally relates to system and method for the on-machine 3-D depth measurement.
2. Description of the Prior Art
With the development of the high technology and high precision industries, the size of parts has become smaller and smaller, and accuracy has also become much finer. In order to further enhance the accuracy of micro manufacture, an adequate error measurement method that can identify the milling errors of micro workpiece is necessary. However, because of the tighter accuracy requirement, miniaturized size of machined workpiece, and higher efficiency of manufacture, the measurement method should contain the characteristic of non-contact, real time, and on-machine.
The 3-D formation modeling in the mechanical vision field, as shown in FIG. 1, employs the concept that two parallel cameras, in a relative distance b (baseline distance), take pictures respectively, the coordinates Pl, Pr in the planes of the right and left image are obtained for the object point P, and value of Z is analyzed in the similar triangle theory:
                    z        =                  bf                                                                x                l                ′                            -                              x                r                ′                                                                                    (        1        )            
and                |x′l−x′r|: the parallax of the same object point in two images        f: the focus of the camera        
Because the size of a camera is fixed, the visual field is smaller when the resolution is higher for the camera set sold in the current market if the 3-D formation theory is employed to calculate the depth of a micro device. To work in the image retrieving condition for a high resolution, the relative distance B cannot be too long because of the limitation of the scope of the visual field. That factor further affects the precision of the depth-pixel resolution (the object depth per pixel parallax unit) when measuring, because the parallax is too small. Therefore, the depth value cannot be calculated precisely so as not to meet the requirement of the depth measurement of the high-precision micro device usually because of the insufficient depth-pixel resolution, if the general camera set adopting the 3-D formation theory is employed to calculate the depth of the micro device.